1. Field of the Invention
This invention relates to a web handling method to prevent web drive components from becoming contaminated by insufficiently dried portions of the web.
2. Description of the Prior Art
In the manufacture of numerous products liquid compositions are coated on a continuous web. The coated surface of the web is then subjected to controlled temperatures and humidities to effect setting and drying. Depending on the particular path that the web must follow during processing, it may be necessary or expeditious for the web's coated surface to contact rollers which guide the web along a given path. In such processes, it is important that the web be completely dried prior to contacting a roller or windup to prevent roller or interweb contamination. If there are portions of the web that have not been completely dried, the rollers will be contaminated and will in turn contaminate subsequent sections of the web passing over them. If portions of the coated web are not completely dried when wound up, they can stick to the underside of the web that lies on top. In this way, large portions may become unacceptably contaminated.
This contamination is a particular problem in the manufacture of photographic materials where coating compositions are applied to various supports such as paper or film. In order to obtain the high coating speeds needed in today's competitive environment it is essential that the coating operation be a continuous uninterrupted process. This is obtained by the use of complex equipment which the trailing edge of one web to the leading edge of another web without stopping the web and its transport system. It is possible that the coating procedure may be disrupted when a splice passes the coating station. In general when a coating process starts or is disturbed the coating is nonuniform and includes thicker regions.
Since dryers are designed with a capacity adequate to dry the normal coating to the desired dryness, heavier or thicker web coatings due to start-up or disturbance of the process often are insufficiently dried.
Some known methods to alleviate this problem are the use of a suction device adjacent the coating apparatus which acts as a vacuum cleaner on demand to suction off excess fluid from the web surface. This, however, requires cleaning of the suction tube after each operation to ensure that there are no lingering specks particles of the coasting material which may dry out and impede the sectioning system.
In EP 0 254 306 a multi-roll web support arrangement is described which is adapted to evacuate the excess fluid from the web surface. This arrangement has some major disadvantages. When the set of rollers is rotated the path of the web changes and lengthens slightly. In order to deal with these variations in pathlength and tension on the web, the web handling device has to be made more complex. The outer surface of the blotting rollers has to be cleaned or changed after one or more operations. These disadvantages make the arrangement described not desirable in a modern and automatic production plant.
As an alternative, the drying capacity of the dryer could be increased to handle the excess material on the web. However, this is inefficient and can lead to excessive drying of a normal coating.